Tuesday, September 23, 2014

It goes without saying that a chimpanzee raised to interact with humans will act differently than other chimps. But according to new research, those effects can last for decades after a chimp is moved to a healthy sanctuary — and being the pet of a loving family (which is legal in most states) could actually be worse for the animals than working as performers.

In a new study published in PeerJ, researchers at the Lincoln Park Zoo attempt to move beyond categorizing chimps as either "human reared" or "mother reared." Instead, they looked at a full spectrum of chimp vs. human interaction. On one end of the spectrum, chimps were completely isolated from members of their own species for the first four years of life, living instead with humans. On the other, they had little or no interaction with humans.

It wasn't all bad news: Surprisingly, the researchers didn't find increased aggression or anxiety in the chimps towards the human end of the spectrum. But they saw big differences in social grooming behavior (that is, where chimps groom each other), which scientists believe to be of incredible importance in chimpanzee communities.

Are chimpanzees naturally violent to one another, or has the intrusion of humans into their environment made them aggressive?

A study published Wednesday in Nature is setting off a new round of debate on the issue.

The study’s authors argue that a review of all known cases of when chimpanzees or bonobos in Africa killed members of their own species shows that violence is a natural part of chimpanzee behavior and not a result of actions by humans that push chimpanzee aggression to lethal attacks. The researchers say their analysis supports the idea that warlike violence in chimpanzees is a natural behavior that evolved because it could provide more resources or territory to the killers, at little risk.

But critics say the data shows no such thing, largely because the measures of human impact on chimpanzees are inadequate.

While the study is about chimpanzees, it is also the latest salvo in a long argument about the nature of violence in people.